1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
Electrophotography has recently shown significant development, so extremely sophisticated characteristics have been requested of electrophotographic photosensitive members. For example, the process speeds of the electrophotographic photosensitive members are increasing year after year, so demands for the potential characteristics of the electrophotographic photosensitive members have become more and more stringent. In addition, an improvement in image quality typified by colorization has been requested of each of the electrophotographic photosensitive members in recent years; with the advent of the representation with colors, the number of halftone images and solid images typified by photographs has been increasing, and the quality of any such image is improving year after year without cessation. For example, an allowable range for the following phenomenon, i.e., the so-called positive ghost image has become markedly limited as compared to that in the case of a monochromatic printer or monochromatic copying machine: when a portion irradiated with light in one image is turned into a halftone image in a subsequent rotation of any one of the electrophotographic photosensitive members, the density of only the portion irradiated with light increases.
The constitutions of the electrophotographic photosensitive members are classified into: a constitution in which a laminate type photosensitive layer formed of a charge generation layer containing a charge-generating substance such as an azo pigment or a phthalocyanine pigment and a hole transport layer containing a hole-transporting substance such as a hydrazone compound, a triarylamine compound, or a stilbene compound is provided on a conductive support; and a constitution in which a single-layer type photosensitive layer containing both the charge-generating substance and the hole-transporting substance is provided on the conductive support. However, merely providing any such photosensitive layer on the conductive support is often responsible for such problems as described below: the photosensitive layer peels, or defects (including form defects such as flaws and material defects such as impurities) in the surface of the conductive support are directly reflected in an image formed with any one of the electrophotographic photosensitive members, so black-dot image defects or blank dots occur. A layer called an intermediate layer has been provided between the photosensitive layer and conductive support of each of many electrophotographic photosensitive members to compensate for such problems. However, some of the electrophotographic photosensitive members show deterioration of their characteristics probably due to the intermediate layer, so attempts have been made to improve the characteristics of the intermediate layer with various approaches (Japanese Patent Application Laid-open No. Hei 9-015889, Japanese Patent Application Laid-open No. Hei 9-258468, Japanese Patent Application Laid-open No. Hei 9-197702, and Japanese Patent Application Laid-open No. Hei 9-127716). Of the approaches, the use of a thermosetting resin or polyvinyl butyral as a resin for the intermediate layer has been adopted, but the approach has not arrived at a level enough to satisfy the recent stringent request for the characteristics.
Meanwhile, for example, a polyolefin resin has been known to serve as a resin excellent in dielectric characteristic, but no proposals have been made on the use of the resin in an intermediate layer for an electrophotographic photosensitive member, the intermediate layer satisfying all required characteristics such as a coating characteristic, solvent resistance, and an electrophotographic characteristic.